Synthesis of polyamines, which are essential to tissue growth and proliferation, is sensitively controlled by the activity of the enzyme, ornithine decarboxylase. The object of this study is to elucidate, in detail, the mechanism of regulation of ornithine decarboxylase in eukaryotes, and the factors which influence the rate of polyamine synthesis. Through this understanding we wish to be able to design and test methods of controlling in vivo synthesis of these compounds. We have shown that the regulation of polyamine synthesis in eukaryotes involves two physically distinct forms of this enzyme, which differ in their activity in physiological levels of the coenzyme, pyridoxal 5'-phosphate, and their stability in vivo and in vitro. The proposed research will involve the complete characterization of these forms, their mechanism of interconversion and degradation, and the exact role played by these forms in the regulation of polyamine synthesis. The separation and purification of the ornithine decarboxylase forms is by normal protein chemistry (ammonium sulfate precipitation, ion exchange and molecular sieve column chromatography, SDS gel electrophoresis, and isoelectric focusing). Characterization will be in terms of subunit structure and molecular weight of active enzyme, kinetics with respect to substrate and coenzyme affinity, titratable SH groups, phosphate content, and vulnerability to proteolytic enzymes. The partially purified and separated enzyme forms will be used as substrate for the assay of the interconverting and the inactivating factors. The role of effector molecules in modifying the activity of these regulatory mechanisms will be explored in vitro and in vivo. The detailed analysis of the regulation of this enzyme will be performed on the readily available enzyme from the primitive eukaryote, Physarum polycephalum, while a similar investigation, initially in less detail, will be made of the two enzyme forms in Chinese hamster ovary and rat liver cells.